Pixel structure, image sensor, and Method for Controlling Image Sensor

ABSTRACT

A pixel structure, an image sensor, an electronic device and a method for controlling an image sensor are provided. The pixel structure includes a plurality of pixel units arranged in an array, each pixel unit includes a first photoelectric conversion element first transfer transistor, coupled to a first floating diffusion region, for transferring charges in the first photoelectric conversion element to the first floating diffusion region; a second photoelectric conversion element, where the sensitivity of the second photoelectric conversion element is lower than that of the first photoelectric conversion element; a second transfer transistor, coupled to a second floating diffusion region, for transferring charges in the second photoelectric conversion element to the second floating diffusion region; and a reading circuit, coupled to the first floating diffusion region and the second floating diffusion region, for reading voltage signals of the first floating diffusion region and the second floating diffusion region

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefits of priority to Chinese PatentApplication No. CN 202210225684X, entitled “Pixel Structure, ImageSensor, Electronic Device and Method for Controlling An Image Sensor”,filed with CN IPA on Mar. 09, 2022, and also claims the benefits ofprionty to Chinese Patent Application No. CN 2022204971211, entitled“Pixel Structure, Image Sensor, and Electronic Device”, filed with CNIPA on Mar. 09, 2022, the content of which is incorporated herein byreference in its entirety.

FIELD OF TECHNOLOGY

The invention relates to the field of image sensing, and morespecifically, to a pixel structure, an image sensor, and a method forcontrolling an image sensor.

BACKGROUND

Image sensors are an important part of a digital camera. Image sensorsare mainly divided into two types: charge coupled devices (CCD) andcomplementary metal oxide semiconductor (CMOS). With the continuousdevelopment of a CMOS integrated circuit manufacturing process,especially the design and manufacturing process of the CMOS imagesensors, the CMOS image sensors has gradually replaced the CCD imagesensors. Compared with the CCD image sensors, CMOS image sensors hascontinued to advance at great pace. For example, the demands of higherresolution and lower power consumption have encouraged the furtherminiaturization and integration of these image sensors. However,miniaturization has come with the loss of pixel photo-sensitivity anddynamic range which require new approaches in order to mitigate.

Currently, standard image sensors have a limited dynamic range of 60 dBto 70 dB. However, the dynamic range of the brightness in the real worldis much wider. The dynamic range of the brightness of natural scenesexceeds 90 dB. To capture both strong light and weak lightsimultaneously, high dynamic range (HDR) technology has been applied toimage sensors to increase the dynamic range of the image sensors. Themost common technique to increase the dynamic range is to combinemultiple exposure images captured by standard image sensors (with a lowdynamic range) into a single linear HDR image. The single linear H DRimage has a much wider dynamic range than a single exposure image.However, it is difficult to effectively improve the dynamic range of theimage sensors while maintaining the performance of the image sensors inthe prior art. In addition, sometimes it is necessary to photographenvironments with flickering, such as vehicles equipped with imagesensors for recognizing traffic signs, traffic signs include signallights composed of LED lights with extremely high flickering frequency.The traditional in-vehicle image sensors adopt a single pixel foridentifying the brightness with a limited dynamic range. In severalapplications, such as automotive applications, the roughly 60 dB dynamicrange of a standard CMOS image sensor does not allow retention of allthe relevant information content of a captured scene, for example,strong light information and weak light information. This will lead tomisjudgment of traffic signs, thereby leading to traffic accidents.

SUMMARY

The present disclosure provides a pixel structure; the pixel structurecomprises a plurality of pixel units arranged in an array, each pixelunit comprises a first photoelectric conversion element, a firsttransfer transistor, coupled to a first floating diffusion region, fortransferring charges in the first photoelectric conversion element tothe first floating diffusion region; a second photoelectnc conversionelement, the sensitivity of the second photoelectric conversion elementis lower than that of the first photoelectric conversion element, asecond transfer transistor, coupled to a second floating diffusionregion, for transferring charges in the second photoelectric conversionelement to the second floating diffusion region; a reading circuit,coupled to the first floating diffusion region and the second floatingdiffusion region, for reading voltage signals of the first floatingdiffusion region and the second floating diffusion region.

The present disclosure provides an image sensor, and the image sensorcomprises a pixel structure as described above.

The present disclosure provides an electronic device, and the electronicdevice comprises an image sensor as described above.

The present disclosure provides a method for controlling an imagesensor, applicable to the image sensor as described above. The methodcomprises: reading information of a first pixel, the first pixelcomprises a first photoelectnc conversion element and a first transfertransistor, and the step of reading the information of a first pixelcomprises: resetting a storage region of the first pixel, and quantizingto obtain a first reset signal; transferring image information of thefirst photoelectric conversion element, and quantizing to obtain a firstimage sampling signal; reading information of a second pixel, the secondpixel comprises a second photoelectric conversion element and a secondtransfer transistor, the step of reading information of a second pixelcompnses: transferring image information of the second photoelectricconversion element, and quantizing to obtain a second image samplingsignal; wherein, a first actual image signal of the first pixel isobtained based on the first reset signal and the first image samplingsignal, and a second actual image signal of the second pixel is obtainedbased on the second image sampling signal.

As described above, the pixel structure, the image sensor, and themethod for controlling the image sensor in the present disclosure havethe following beneficial effects:

The present disclosure adopts the first photoelectric conversion elementand the second photoelectric conversion element, which have differentsensitivities. The first photoelectric conversion element has highsensitivity (due to, e.g., a large area), which is mainly used to obtainweak light information, and the second photoelectric conversion elementhas low sensitivity (due to, e.g., a small area), which is mainly usedto obtain strong light information. Therefore, the image sensor of thepresent disclosure is able to recognize strong light information and lowlight information, which improves its dynamic range.

The present disclosure designs the layout of the pixel structure, whichmay effectively reduce a signal noise, improve a reading accuracy, andreduce the amount of electrons flowing from the first photoelectricconversion element (e.g., with a relatively larger area) to the secondphotoelectric conversion element (e.g., with a relatively smaller area),thereby improving the performance of the image sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a circuit principle of a pixelstructure according to Embodiment 1 of the present disclosure.

FIG. 2 and FIG. 3 are structural diagrams of the layout of a pixelstructure according to Embodiment 1 of the present disclosure.

FIG. 4 is a timing diagram of reading a second pixel and reading a firstpixel in a low conversion gain mode according to Embodiment 1 of thepresent disclosure.

FIG. 5 is a timing diagram of reading a second pixel and reading a firstpixel in a high conversion gain mode according to Embodiment 1 of thepresent disclosure.

FIG. 6 is a timing diagram of reading a first pixel and a second pixelin a low and high conversion gain mode according to Embodiment 1 of thepresent disclosure.

FIG. 7 is a timing diagram of reading a first pixel and a second pixelin a low and high conversion gain mode according to Embodiment 1 of thepresent disclosure.

FIG. 8 is a schematic diagram of a circuit principle of a pixelstructure according to Embodiment 2 of the present disclosure.

FIG. 9 and FIG. 10 are structural diagrams of the layout of a pixelstructure according to Embodiment 2 of the present disclosure.

FIG. 11 is a timing diagram of reading a first pixel and a second pixelin a low and high conversion gain mode according to Embodiment 2 of thepresent disclosure.

FIG. 12 is a timing diagram of reading a first pixel and a second pixelin a low and high conversion gain mode according to Embodiment 2 of thepresent disclosure.

Reference Numerals 100, 400 First pixel 200, 500 Second pixel 300, 600Third pixel PD1, PD3 First photoelectric conversion element TX1, TX3First transfer transistor PD2, PD4 Second photoelectric conversionelement TX2, TX4 Second transfer transistor RST1 First reset transistorSF1 First source follower transistor SEL1 First row select transistorRST2 Second reset transistor SF2 Second source follower transistor SEL2Second row select transistor DCG1, DCG2 Dual conversion gain controltransistor C1, C2 Capacitor SUB Substrate contact SW Switchingtransistor RST3 Reset transistor SF3 Source follower transistor SEL3 Rowselect transistor

DETAILED DESCRIPTION

The implementations of the present disclosure are described belowthrough specific examples. Those skilled in the art can easilyunderstand the other advantages and effects of the present disclosurefrom the content disclosed in this specification. The present disclosuremay also be implemented or applied through other different specificimplementations. Various details in this specification may also bemodified or changed based on different viewpoints and applicationswithout departing from the spirit of the present disclosure.

It should be emphasized that the term “comprise/include” as used hereinrefers to the presence of a feature, whole, step or component, but doesnot exclude the presence or addition of one or more other features,whole, steps or components.

Features described and/or illustrated for one embodiment may be used inthe same or similar manner in one or more other embodiments, incombination with, or replacing certain features in other embodiments.

For example, when describing the embodiments of the present disclosurein detail, for ease of description, a cross-sectional view for showing adevice structure is partially enlarged not necessarily to scale, and theschematic diagram is merely an example and is not intended to limit thescope of the present disclosure. In addition, the three-dimensionalspatial dimensions of length, width and depth should be included in theactual production.

For ease of description, spatial terms, such as “under” “below”,“lower”, “beneath”, “above”, “upper”, and the like, may be used hereinto describe the relationship between one element or feature and anotherelement or feature as shown in the accompanying drawings. It is to beunderstood that these spatial terms are intended to encompass otherdirections of the device in use or operation than the directionsdepicted in the accompanying drawings. In addition, when a layer isreferred to as being “between” two layers, the layer may be the onlylayer between the two layers, or one or more layers may be presenttherebetween.

In the context of this present disclosure, a structure in which a firstfeature is described as being “on” a second feature may include anembodiment in which the first feature and the second feature are indirect contact with each other, or may include an embodiment in whichthere is another feature formed between the first feature and the secondfeature. In other words, the first feature and the second feature maynot be in direct contact with each other.

It should be noted that, the drawings provided in this embodiment onlyexemplify the basic idea of the present disclosure. Although only thecomponents related to the present disclosure are shown in the drawings,they are not drawn according to the quantities, shapes, and sizes of thecomponents during actual implementation. During actual implementation,the patterns, quantities, and proportions of the components may bechanged as needed, and the layout of the components may be morecomplicated.

The traditional in-vehicle image sensors adopt a single pixel foridentifying the brightness with a limited dynamic range. So thetraditional in-vehicle image sensors are unable to identify brightnessinformation out of the dynamic range, for example, strong lightinformation and weak light information. This will lead to misjudgment oftraffic signs, thereby leading to traffic accidents. The presentdisclosure provides a pixel structure, an image sensor, and a method forcontrolling the image sensor. The present disclosure may solve theproblem of a narrow dynamic range of traditional image sensors in theprior art, and a narrow dynamic range makes it difficult to capture weaklight and strong light. In light of the above problem, the presentdisclosure provides a pixel structure. The pixel structure indudes aplurality of pixel units arranged in an array. Each pixel unit includesa first photoelectric conversion element; a first transfer transistor,coupled to a first floating diffusion region, for transferring chargesin the first photoelectric conversion element to the first floatingdiffusion region; a second photoelectric conversion element, thesensitivity of the second photoelectric conversion element is lower thanthat of the first photoelectric conversion element; a second transfertransistor, coupled to a second floating diffusion region, fortransferring charges in the second photoelectric conversion element tothe second floating diffusion region; and a reading circuit, coupled tothe first floating diffusion region and the second floating diffusionregion, for reading voltage signals of the first floating diffusionregion and the second floating diffusion region. The sensitivity of thesecond photoelectric conversion element is lower than that of the firstphotoelectric conversion element. For example, a photosensitive area ofthe second photoelectric conversion element may be set to be smallerthan that of the first photoelectric conversion element, so that thefirst photoelectric conversion element may be used to obtain weak lightinformation, and the second photoelectric conversion element may be usedto obtain strong light information, so that the image sensor may becompatible to recognize weak light information and strong lightinformation. Therefore, the dynamic range of the image sensor isimproved. In other embodiments, the sensitivity of the secondphotoelectric conversion element is set lower than that of the firstphotoelectric conversion element in other ways. For example, anattenuation layer is disposed on the second photoelectric conversionelement, etc., and the present disclosure is not limited to exampleslisted herein.

Embodiment 1

As shown in FIGS. 1-3 , a pixel structure is provided in the embodimentThe pixel structure includes a plurality of pixel units arranged in anarray. Each pixel unit includes a first photoelectric conversion elementPD1, a first transfer transistor TX1, a second photoelectnc conversionelement PD2, a second transfer transistor TX2 and a reading circuit.

The first photoelectric conversion element PD1 is used to capture weaklight, and is used to convert light signals (e.g., weak light) intoelectrical signals. The function of the first photoelectric conversionelement PD1 may be set based on an actual situation of a captured scene.The first photoelectric conversion element PD1 includes a photodiode,for example, a PPD type photodiode.

The first transfer transistor TX1 is coupled to a first floatingdiffusion region, and is for transferring charges in the firstphotoelectric conversion element PD1 to the first floating diffusionregion. In an embodiment, the first floating diffusion region is ashared charge collection region; in other embodiments, the firstfloating diffusion region includes several floating diffusion points,and the sum of charges collected by all floating diffusion points arecharges collected by the first floating diffusion region. The firstphotoelectric conversion element PD1, the first transfer transistor TX1and the first floating diffusion region may adopt existing structures inprior art.

The sensitivity of the second photoelectric conversion element PD2 islower than that of the first photoelectric conversion element PD1. Thesecond photoelectric conversion element PD2 is used to capture stronglight, and is used to convert light signals (e.g., strong light) intoelectrical signals. The second photoelectric conversion element PD2includes a photodiode, for example, a PPD type photodiode.

The second transfer transistor TX2 is coupled to a second floatingdiffusion region, and is for transferring charges in the secondphotoelectric conversion element PD2 to the second floating diffusionregion. In some embodiments, the second floating diffusion region is ashared charge collection region; in other embodiments, the secondfloating diffusion region includes several floating diffusion points,and the sum of charges collected by all floating diffusion points arecharges collected by the second floating diffusion region. The secondphotoelectric conversion element PD2, the second transfer transistor TX2and the second floating diffusion region may adopt existing structuresin prior art.

As shown in FIG. 1 , the reading circuit includes a first resettransistor RST1, a first source follower transistor SF1, a second resettransistor RST2 and a second source follower transistor SF2. In someembodiments, the above transistors are N type Metal-Oxide-Semiconductor(NMOS) transistors.

A source of the first reset transistor RST1 is coupled to the firstfloating diffusion region, and a drain of the first reset transistorRST1 is coupled to a first voltage terminal, so as to reset the firstfloating diffusion region. A gate of the first reset transistor RST1 isconnected to a first reset signal terminal, so as to reset the firstfloating diffusion region under the control of a first reset signalprovided by the first reset signal terminal

A gate of the first source follower transistor SF1 is coupled to thefirst floating diffusion region, a drain of the first source followertransistor SF1 is coupled to a second voltage terminal, and a source ofthe first source follower transistor SF1 is coupled to a first outputline.

A source of the second reset transistor RST2 is coupled to the secondfloating diffusion region, and a drain of the second reset transistorRST2 is coupled to a third voltage terminal, so as to reset the secondfloating diffusion region. A gate of the second reset transistor RST2 isconnected to a second reset signal terminal, so as to reset the secondfloating diffusion region under the control of a second reset signalprovided by the first reset signal terminal.

A gate of the second source follower transistor SF2 is coupled to thesecond floating diffusion region, a drain of the second source followertransistor SF2 is coupled to a fourth voltage terminal, and a source ofthe second source follower transistor SF2 is coupled to a second outputline

The first output line and the second output line may be two differentoutput lines or a shared output line, which determines whether thesignals are output in parallel or in serial. In an embodiment, thesecond output line and the first output line are a shared output lineBIT

In one embodiment, the first voltage terminal, the second voltageterminal, the third voltage terminal and the fourth voltage terminal arethe same voltage terminal VDD, so as to simplify circuit design andwiring. The above setting may save cost and improve the accuracy ofsignals.

In an embodiment, the reading circuit further includes a doubleconversion gain control transistor DCG1. The double conversion gaincontrol transistor DCG1 is coupled between the first floating diffusionregion and the first reset transistor RST1 to improve a dynamic range ofthe pixel structure. The double conversion gain control transistor DCG1may be an NMOS transistor. In addition, a capacitor may also be setbetween the first reset transistor RST1 and the double conversion gaincontrol transistor DCG1, and the capacitor may be a parasitic capacitoror a device capacitor A low conversion gain mode and a high conversiongain mode may be switched to each other by turning on and turning offthe double conversion gain control transistor DCG1.

In an embodiment, the reading circuit includes a first row selecttransistor SEL1. A drain of the first row select transistor SEL1 iscoupled to the source of the first source follower transistor SF1, and asource of the first row select transistor SEL1 is coupled to the firstoutput line. The first row select transistor SEL1 adopts an NMOStransistor.

In an embodiment, the reading circuit includes a second row selecttransistor SEL2. A drain of the second row select transistor SEL2 iscoupled to the source of the second source follower transistor SF2, anda source of the second row select transistor SEL2 is coupled to thesecond output line. The second row select transistor SEL2 adopts an NMOStransistor.

It should be noted that the ratio of the number of the first pixel tothe number of the second pixel may be the ratio of the number of thefirst photoelectric conversion element PD1 and the number of the secondphotoelectric conversion element PD2. The ratio of the number of thefirst photoelectric conversion element PD1 and the number of the secondphotoelectric conversion element PD2 may be set according to actualneeds. For example, the ratio is 1:1, 2:1, 4:1. and the like. In theembodiment, as shown in FIG. 2 and FIG. 3 , the ratio is 1:1.

In an embodiment, as shown in FIG. 2 and FIG. 3 , the first pixel 100includes the first photoelectric conversion element PD1, the firsttransfer transistor TX1, the first floating diffusion region, the firstreset transistor RST1, the first source follower transistor SF1 and thefirst row select transistor SEL1. And multiple first pixels arranged ina first direction. The second pixel 200 includes the secondphotoelectric conversion element PD2, the second transfer transistorTX2, the second floating diffusion region, the second reset transistorRST2, the second source follower transistor SF2 and the second rowselect transistor SEL2. And multiple second pixels arranged in the firstdirection. A plurality of first pixels 100 are arranged in an array, anda plurality of second pixels 200 are arranged in an array.

In an embodiment, multiple first pixels are arranged in rows along thefirst direction, and are arranged in columns along a second direction.Optionally, the first direction is perpendicular to the seconddirection. Meanwhile, multiple second pixels are arranged in rows alongthe first direction, and are arranged in columns along the seconddirection. In addition, projections of each first photoelectricconversion element of first pixels in the first direction andprojections of each second photoelectric conversion element of secondpixels in the first direction are alternately arranged, and projectionsof each first photoelectric conversion element in first pixels in thesecond direction and projections of each second photoelectric conversionelement in second pixels in the second direction are alternatelyarranged.

In an embodiment, the first pixel 100 and the second pixel 200 adjacentto the first pixel 100 form a pixel unit, and a distance between aprojection of the first row select transistor SEL1 of the first pixel100 in the first direction and a projection of the second row selecttransistor SEL2 of the second pixel 200 in the first direction isshorter than distances between the projection of the first row selecttransistor SEL1 of the first pixel 100 in the first direction andprojections of second row select transistors of other pixels in thefirst direction. As shown in FIG. 2 , the first row select transistorSEL1 is selected first. The second row select transistor SEL2 isselected because the distance D1 between the projection of the first rowselect transistor SEL1 of the first pixel 100 in the first direction andthe projection of the second row select transistor SEL2 of the secondpixel 200 in the first direction is shorter than distances between theprojection of the first row select transistor SEL1 of the first pixel100 in the first direction and projections of second row selecttransistors of other pixels in the first direction. Therefore, the firstpixel 100 including the first row select transistor SEL1 and the secondpixel 200 including the second row select transistor SEL2 are selectedto form the pixel unit. The distance D1 is shown in FIG. 3 . Based onthe above description, any one of the two pixels (e.g., including thefirst pixel 100 and a third pixel 300, for ease of description, whereinanother first pixel adjacent to the second pixel 200 in FIGS. 2-3 isreferred to as the third pixel 300) adjacent to the second pixel 200 andthe second pixel 200 form the pixel unit, which facilitates wiring ofthe pixel unit and the transmission of image signals.

In an further embodiment, the first row select transistor SEL1 and thesecond row select transistor SEL2 share the output line BIT, and thedistance D1 is shorter, which facilitates the wiring of the output lineBIT in the pixel unit. The setting of the output line BIT may reducesignal noise and improve readout accuracy.

In an embodiment, as shown in FIG. 3 , in one pixel unit, a distance D2between the first source follower transistor SF1 of the first pixel 100and the second pixel 200 is set to be less than a distance D3 betweenthe first row select transistor SEL1 of the first pixel 100 and thesecond pixel 200. This setting makes the first source followertransistor SF1 of the first pixel 100 adjacent to the first floatingdiffusion region, to facilitate the output of the first floatingdiffusion region, improve the signal conversion gain, and reduce thenoise. In an embodiment, the distance D2 is a distance between the firstsource follower transistor SF1 of the first pixel 100 and the second rowselect transistor SEL2 of the second pixel 200; the distance D3 is adistance between the first row select transistor SEL1 of the first pixel100 and the second row select transistor SEL2 of the second pixel 200.

In the two pixels (the first pixel 100 and the third pixel 300) adjacentto the second pixel 200, the distance D1 between the projection of thefirst row select transistor SEL1 of the first pixel 100 in the firstdirection and the projection of the second row select transistor SEL2 ofthe first pixel 200 in the first direction is equal to that between aprojection of a third row select transistor (not labeled in FIGS. 2-3 )of the third pixel 300 in the first direction and the projection of thesecond row select transistor SEL2 of the first pixel 200 in the firstdirection. However, the distance between the first source followertransistor SF1 of the first pixel 100 and the second pixel 200 isshorter than that between the source follower transistor of the thirdpixel 300 and the second pixel 200. Therefore, the first pixel 100 andthe second pixel 200 form the pixel unit in the embodiment, to obtain abetter layout and improve the performance of the image sensor.

In an embodiment, as shown in FIG. 2 , each second photoelectricconversion element PD2 is disposed at a center of a pattern formed byfour first photoelectric conversion elements PD1 arranged in an array,and the second transfer transistor TX2, the second reset transistorRST2, the second source follower transistor SF2, and the second rowselect transistor SEL2 are sequentially arranged between two adjacentsecond photoelectric conversion elements PD2 along the first direction.In another embodiment, the first reset transistor RST1, the first sourcefollower transistor SF1, and the first row select transistor SEL1 arearranged between two adjacent second photoelectric conversion elementsPD2 along the second direction perpendicular to the first direction.Further, each of four corner regions of each first photoelectricconversion element PD1 (in this embodiment, PD1 has four corners) isalso correspondingly provided with a second photoelectric conversionelement PD2, and each of four corner regions of each secondphotoelectric conversion element PD2(in this embodiment, PD2 has fourcorners) is also correspondingly provided with a first photoelectricconversion element PD1.

In an embodiment, when the pixel unit further includes a dual conversiongain control transistor DCG1. The dual conversion gain controltransistor DCG1 and the first reset transistor RST1 are arranged in acolumn along the second direction, the first source follower transistorSF1 and the first row select transistor SEL1 are arranged in a columnalong the second direction, and the dual conversion gain controltransistor DCG1 and the first reset transistor RST1 are arranged closeto the first photoelectric conversion element PD1 in a same pixel unit.Among them, the gain control transistor DCG1. the first reset transistorRST1 and the first photoelectric conversion element PD1 are arranged inthe first pixel 100.

In an embodiment, the pixel unit further includes a substrate contactSUB. The substrate contact SUB is disposed on a side of the first rowselect transistor SEL1 along the second direction, the side of the firstrow select transistor SEL1 is facing away from the first source followertransistor SF1 Under a certain potential, a potential barrier for theflow of electrons is formed on the substrate contact SUB, and thepotential barrier may effectively block the leakage of electrons in thefirst pixel 100 to the surrounding second pixels 200, isolating thefirst pixel 100 from the second pixel 200.

In an embodiment, in one pixel unit, a distance between a projection ofa center of the first photoelectric conversion element PD1 in the seconddirection and a projection of a center of the second photoelectricconversion element PD2 in the second direction is a first distance L1.In two adjacent pixel units, a distance between a projection of a centerof the first photoelectric conversion element PD1 of one pixel unit inthe second direction and a projection of a center of the secondphotoelectric conversion element PD2 of the other pixel unit in thesecond direction is a second distance L2. The first distance L1 islarger than the second distance L2 In the embodiment, in one pixel unit,the first photoelectric conversion element PD1 is relatively far awayfrom the second photoelectric conversion element PD2, so that whenelectrons are being leaked, paths for electrons to leak from the firstphotoelectnc conversion element PD1 to the second photoelectricconversion element PD2 are also longer, so that leaked electrons aremore easily absorbed by the voltage terminal VDD of the same firstpixel. That is, because the voltage terminal VDD is closer to the firstphotoelectric conversion element PD1, part of electrons leaked from thefirst photoelectric conversion element PD1 flows to the voltage terminalVDD. Therefore, the number of electrons leaked from the firstphotoelectric conversion element PD1 to the second photoelectricconversion element PD2 is reduced, which improve the image accuracy.

In an embodiment, in one pixel unit, a distance between the projectionof the center of the first photoelectric conversion element PD1 in thefirst direction and the projection of the center of the secondphotoelectric conversion element PD2 in the first direction is a thirddistance M1. In two adjacent pixel units, a distance between theprojection of the center of the first photoelectric conversion elementPD1 of one pixel unit in the first direction and the projection of thecenter of the second photoelectric conversion element PD2 of the otherpixel unit in the first direction is a fourth distance M2. The thirddistance M1 is equal to the fourth distance M2.

In an embodiment, an area of the first photoelectric conversion elementPD1 is larger than that of the second photoelectric conversion elementPD2, so that the sensitivity of the second photoelectric conversionelement PD2 is lower than that of the first photoelectric conversionelement PD1.

In an embodiment, the pixel structure also includes one or more anattenuation layers, and there is at least one anti-reflection layerdisposed between the second photoelectric conversion element PD2 and anincident light, so that the sensitivity of the second photoelectricconversion element PD2 is lower than that of the first photoelectricconversion element PD1. The attenuation layer may adopt existingattenuation structures. For example, an material layer, or a metal gridare arranged between the photoelectric conversion element and theincident light. The attenuation layer is facing a light-receivingsurface of the second photoelectric conversion element PD2. In anotherembodiment, the attenuation layer may be further extended to the firstphotoelectric conversion element PD1.

In an embodiment, in one pixel unit, the first pixel 100 and the secondpixel 200 are respectively provided with a color filter of the samecolor. For example, multiple first pixels 100 may form a Bayer arrayarrangement, and multiple second pixels 200 may form a Bayer arrayarrangement. The other color filters may be configured according toactual needs. In the embodiment, the first pixel 100 and the secondpixel 200 of one pixel unit are respectively provided with a colorfilter of the same color. That is, color filters of the same color areconfigured on the first photoelectric conversion element PD1 and thesecond photoelectric conversion element PD2 in one pixel unit.

In an embodiment, in one pixel unit, the first pixel 100 corresponds toa first lens, and the second pixel 200 corresponds to a second lens. Inthe embodiment, each of the first pixels 100 corresponds to acorresponding one of the first lenses, and each of the second pixels 200corresponds to a corresponding one of the second lenses. The first lensand the second lens may be different, for example, the height of thefirst lens is different from that of the second lens.

In an embodiment, as shown in FIG. 1 , the pixel unit includes a chargestorage device. A terminal of the charge storage device is coupled tothe second floating diffusion region, and the other terminal of thecharge storage device is connected to ground or a variable voltage.

In an embodiment, the charge storage device is a capacitor C1. Thecharge storage device is used to storage charges generated by the secondphotoelectric conversion element PD2, to increase a full well capacityof the second pixel 200 and to reduce the sensitivity of thephotoelectric conversion element. Optionally, the capacitor C1 is adevice capacitance or a parasitic capacitance.

The present disclosure also provides an image sensor. The image sensorincludes the pixel structure descnbed in the above embodiments. Theimage sensor further includes a peripheral logic circuit for receivingand processing signals output by the reading circuit of the pixelstructure. The image sensor may be a complementary metal oxidesemiconductor (CMOS) image sensor, or may be other image sensors thatmay use pixel structures described in the above embodiments.

The present disclosure also provides an electronic device is provided.The electronic device includes the image sensor described in the aboveembodiments. The electronic device may be a mobile device, a digitalcamera, a medical device, or a computer. The electronic device includesthe image sensor. The specific structure of the image sensor refers tothe above embodiments. Since the electronic device adopts all thetechnical solutions of all the above embodiments, it has at least allthe beneficial effects brought by the technical solutions of the aboveembodiments. In addition, the electronic equipment may also bemonitoring equipment, machine vision related device, UAV, mobile phones,cameras, and the like.

As shown in FIGS. 4-7 , the present disclosure also provides a methodfor controlling an image sensor, which is applicable to the image sensordescribed in the above embodiments. The method includes step 110 andstep 120.

Step 110, reading information of the first pixel 100, where the firstpixel 100 includes the first photoelectric conversion element PD1 andthe first transfer transistor TX1. The step 110 of reading informationof the first pixel 100 includes step 111 and step 112.

Step 111, resetting a storage region of the first pixel 100, andquantizing it to obtain a first reset signal Vrst1. In one embodiment,the quantizing is performed by an analogue-to-digital converter, orother hardware or software that is capable of implementing signalconversion, and the first reset signal Vrst1 includes information of thestorage region; the term “quantizing” hereinafter may be interpreted ina similar way.

Step 112, transferring image information of the first photoelectricconversion element PD1, and quantizing it to obtain a first imagesampling signal Vsig1.

Step 120, reading information of the second pixel 200, where the secondpixel 200 includes the second photoelectric conversion element PD2 andthe second transfer transistor TX2. The step 120 of reading informationof the second pixel 200 includes step 121.

Step 121, transferring image information of the first photoelectricconversion element PD2, and quantizing it to obtain a second imagesampling signal Vsig2.

A first actual image signal of the first pixel 100 is obtained based onthe first reset signal Vrst1 and the first image sampling signal Vsig1,and a second actual image signal of the second pixel 200 is obtainedbased on the second image sampling signal Vsig2. It should be noted thatthe execution sequence of steps 111, 112, and 121 does not strictlyrepresent the execution sequence of each step of the method in thepresent disclosure, and those skilled in the art may change theexecution sequence of the above steps according to actual needs. Basedon a reading mode of the first pixel, a correlation double sampling(CDS) may be realized.

In an embodiment, step 120 of reading information of the second pixel200 also includes:

Step 122, resetting a storage region of the second pixel 200, andquantizing it to obtain a second reset signal Vrst2; and obtaining asecond actual image signal based on the second reset signal Vrst2 andthe second image sampling signal Vsig2

In an embodiment, as shown in FIGS. 4-6 , the step of quantifying thereset signal may be performed after step 121 is performed. In anotherembodiment, as shown in FIG. 7 , the step of quantifying the resetsignal may be performed after step 112 and before step 121. In FIGS. 4-7, 3 µm pixel is an example of the first pixel 100, 1.0 µm pixel is anexample of the second pixel 200.

In an embodiment, the reading mode of the first pixel 100 includes atleast one of a low conversion gain mode and a high conversion gain mode.The first pixel is read in the low conversion gain mode (as shown inFIG. 4 ), or is read in the high conversion gain mode (as shown in FIG.5 ), or is read in both the low conversion gain mode and the highconversion gain mode (as shown in FIG. 6 and FIG. 7 ). The high dynamicrange is achieved in the above reading modes. In an embodiment, the highconversion gain mode and the low conversion gain mode may be realized bypreparing the dual conversion gain transistor DCG1 between the firstreset transistor RST1 and the first floating diffusion region of thefirst pixel. In a further embodiment, the high conversion gain mode andthe low conversion gain mode may be realized by preparing a capacitorbetween the first reset transistor RST1 and the dual conversion gaintransistor DCG1, switching between the high conversion gain mode and thelow conversion gain mode may be realized by turning on or turning offthe dual conversion gain transistor DCG1. In other embodiments, othermethods may be adopted to switch between the high conversion gain modeand the low conversion gain mode.

As shown in FIG. 6 and FIG. 7 , when the first pixel 100 is read in thehigh conversion gain mode and the low conversion gain mode, the methodof reading the first pixel 100 includes following steps:

Step 113, resetting the storage area of the first pixel in the lowconversion gain mode LCG, and quantizing it to obtain the first resetsignal lcgrst1 in the low conversion gain mode LCG.

Step 114, resetting the storage area of the first pixel in the highconversion gain mode HCG, and quantizing it to obtain the first resetsignal hcgrst1 in the high conversion gain mode HCG.

Step 115, transferring image information of the first photoelectricconversion element in the high conversion gain mode HCG, and quantizingit to obtain the first image sampling signal hcgsig1 in the highconversion gain mode HCG.

Step 116, redistributing image information of the first photoelectricconversion element in the low conversion gain mode LCG, and quantizingit to obtain the first image sampling signal lcgsig1 in the lowconversion gain mode LCG.

The first actual image signal of the first pixel is obtained based onthe first reset signal lcgrst1 and the first image sampling signallcgsig1 in the low conversion gain mode, and the first reset signalhcgrst1 and the first image sampling signal hcgsig1 in the highconversion gain mode.

As shown in FIG. 6 , one method of reading the second pixel 200 includesfollowing steps: image information of the second photoelectricconversion element is transferred and the second image sampling signalVsig2 is obtained by quantifying, and then the storage area of thesecond pixel is reset and the second reset signal Vrst2 is obtained byquantifying. As shown in FIG. 7 , another method of reading the secondpixel 200 includes following steps: the storage area of the second pixelis reset, the second reset signal Vrst2 is obtained by quantifying, andthen the image information of the second photoelectric conversionelement is transferred, and the second image sampling signal Vsig2 isobtained by quantifying;and based on this method of reading the secondpixel 200, the CDS may be realized. Other execution sequences of theabove steps may also be used to read out the second pixel

Embodiment 2

As shown in FIGS. 8-10 , the present disclosure provides a pixelstructure. The pixel structure includes a plurality of pixel unitsarranged in an array. Each pixel unit includes a first photoelectricconversion element PD3, a first transfer transistor TX3, a secondphotoelectric conversion element PD4, a second transfer transistor TX4and a reading circuit.

The first photoelectric conversion element PD3 is used to capture weaklight, and is used to convert light signals (e.g., weak light) intoelectrical signals. The function of the first photoelectric conversionelement PD3 may be set based on an actual situation of a captured scene.The first photoelectric conversion element PD3 includes a photodiode,for example, a PPD type photodiode.

The first transfer transistor TX3 is coupled to a first floatingdiffusion region, and is for transferring charges in the firstphotoelectric conversion element PD3 to the first floating diffusionregion. In an embodiment, the first floating diffusion region is ashared charge collection region; in other embodiments, the firstfloating diffusion region includes several floating diffusion points,and the sum of charges collected by all floating diffusion points arecharges collected by the first floating diffusion region The firstphotoelectric conversion element PD3, the first transfer transistor TX3and the first floating diffusion region may adopt existing structures inprior art.

The sensitivity of the second photoelectric conversion element PD4 islower than that of the first photoelectric conversion element PD3. Thesecond photoelectric conversion element PD4 is used to capture stronglight, and is used to convert light signals (e.g., strong light) intoelectrical signals. The second photoelectric conversion element PD4includes a photodiode, for example, a PPD type photodiode.

The second transfer transistor TX4 is coupled to a second floatingdiffusion region, and is for transferring charges in the secondphotoelectric conversion element PD4 to the second floating diffusionregion. In some embodiments, the second floating diffusion region is ashared charge collection region; in other embodiments, the secondfloating diffusion region includes several floating diffusion points,and the sum of charges collected by all floating diffusion points arecharges collected by the second floating diffusion region. The secondphotoelectric conversion element PD4, the second transfer transistor TX4and the second floating diffusion region may adopt existing structuresin prior art.

As shown in FIG. 4 , the reading circuit includes a reset transistorRST3 and a source follower transistor SF3. The reset transistor RST3 andthe source follower transistor SF3 may adopt an NMOS transistor. Asource of the reset transistor RST3 is coupled to the first floatingdiffusion region and the second floating diffusion region respectively,and a drain of the reset transistor RST3 is coupled to a first commonterminal, so as to reset the first floating diffusion region and thesecond floating diffusion region. A gate of the source followertransistor SF3 is coupled to the first floating diffusion region and thesecond floating diffusion region respectively, a drain of the sourcefollower transistor SF3 is coupled to a second common terminal, a sourceof the source follower transistor SF3 is coupled to an output line. Theabove transistors are N type Metal-Oxide-Semiconductor (NMOS)transistors.

In an embodiment, the reading circuit includes a row select transistorSEL3. A drain of the row select transistor SEL3 is coupled to the sourceof the source follower transistor SF3, and a source of the row selecttransistor SEL3 is coupled to the output line. The row select transistorSEL3 may adopts an NMOS transistor.

In an embodiment, the reading circuit further includes a switchingtransistor SW. The source of the reset transistor RST3 is coupled to thesecond floating diffusion region through the switching transistor SW,and the gate of the source follower transistor SF3 is coupled to thesecond floating diffusion region through the switching transistor SW.The output of the second floating diffusion region may be realized byturning off and turning on the switching transistor SW, thereby readingthe first floating diffusion region and the second floating diffusionregion independently. This embodiment may effectively save the number oftransistors in the reading circuit. That is, the first pixel and thesecond pixel may share one reset transistor (e.g, RST3), one sourcefollower transistor (e.g., SF3) and one row select transistor (e.g.,SEL3) after only one switching transistor is added in the readingcircuit, which effectively save an area of the pixel structure andreduce manufacturing costs of an image sensor.

In an embodiment, the reading circuit further includes a doubleconversion gain control transistor DCG2. The double conversion gaincontrol transistor DCG2 is coupled between the first floating diffusionregion and the reset transistor RST3 to improve a dynamic range of thepixel structure. The double conversion gain control transistor DCG2 maybe an NMOS transistor. In addition, a capacitor may also be set betweenthe reset transistor RST3 and the double conversion gain controltransistor DCG2, and the capacitor may be a parasitic capacitor or adevice capacitor A low conversion gain mode and a high conversion gainmode may be switched to each other by turning on and turning off thedouble conversion gain control transistor DCG2.

It should be noted that the ratio of the number of the first pixel tothe number of the second pixel may be the ratio of the number of thefirst photoelectric conversion element PD3 and the number of the secondphotoelectric conversion element PD4. The ratio of the number of thefirst photoelectric conversion element PD3 and the number of the secondphotoelectric conversion element PD4 may be set according to actualneeds. For example, the ratio is 1:1, 2:1, 4:1, and the like. In theembodiment, as shown in FIG. 9 and FIG. 10 , the ratio is 1:1.

In an embodiment, as shown in FIG. 9 and FIG. 10 , the first pixel 400includes the first photoelectric conversion element PD3, the firsttransfer transistor TX3, and the first floating diffusion region. Amongthem, projections of the first photoelectric conversion element PD3, thefirst transfer transistor TX3, and the first floating diffusion regionin a first direction are arranged in the order of the firstphotoelectric conversion element PD3, the first transfer transistor TX3,and the first floating diffusion region. And multiple first pixelsarranged in a first direction. The second pixel 500 includes the secondphotoelectric conversion element PD4, the second transfer transistorTX4, and the second floating diffusion region. Among them, projectionsof the second photoelectric conversion element PD4, the second transfertransistor TX4, and the second floating diffusion region in the firstdirection are arranged in the order of the second photoelectricconversion element PD4, the second transfer transistor TX4, and thesecond floating diffusion region. And multiple second pixels arranged ina first direction A plurality of first pixels 400 are arranged in anarray, and a plurality of second pixels 500 are arranged in an array.

In an embodiment, multiple first pixels are arranged in rows along thefirst direction, and are arranged in columns along a second direction.Optionally, the first direction is perpendicular to the seconddirection. Meanwhile, multiple second pixels are arranged in rows alongthe first direction, and are arranged in columns along the seconddirection. In addition, projections of each first photoelectricconversion element of first pixels in the first direction andprojections of each second photoelectric conversion element of secondpixels in the first direction are alternately arranged, and projectionsof each first photoelectric conversion element in first pixels in thesecond direction and projections of each second photoelectric conversionelement in second pixels in the second direction are alternatelyarranged.

In an embodiment, the first pixel and the second pixel adjacent to thefirst pixel form a pixel unit. among them, a line connecting aprojection of the first floating diffusion region of the first pixel 400in the first direction to a projection of the second floating diffusionregion of the second pixel 500 in the first direction avoids aprojection of the first transfer transistor TX3 in the first direction.As shown in FIG. 9 , any one of the two pixels (e.g., including thefirst pixel 400 and a fourth pixel 700; for ease of description, anotherfirst pixel adjacent to the second pixel 500 in FIGS. 9-10 is referredto as the fourth pixel 700) adjacent to the second pixel 500 and thesecond pixel 500 may form the pixel unit. That is, the second pixel 500forms the pixel unit with the first pixel in the solid-line boxes (e.g.,the first pixel 400, the fourth pixel 700), and does not form the pixelunit with the first pixel in the dotted-line boxes. This alleviates theeffect of the wiring on signal transmission.

As shown in FIG. 9 , when the reading circuit includes the switchingtransistor SW, the switching transistor SW is disposed on a side of thefirst transfer transistor TX3 along the first direction. The side of thefirst transfer transistor TX3 is facing away from the photoelectricconversion element PD3. In an embodiment, the second pixel 500 is firstdetermined. Then the first pixel 400 is selected from multiple pixelsadjacent to the second pixel 500, and adistance between a projection ofthe first floating diffusion region of the first pixel 400 in the firstdirection and a projection of the switching transistor SW of the secondpixel 500 in the first direction is further than distances betweenprojections of the floating diffusion regions of other pixels adjacentto the second pixel 500 in the first direction and the projection of theswitching transistor SW of the second pixel 500 in the first direction.Therefore, the first pixel 400 and the second pixel 500 are selected toform the pixel unit. Because the distance between the projection of thefirst floating diffusion region of the first pixel 400 in the firstdirection and the projection of the switching transistor SW of thesecond pixel 500 in the first direction is relatively large, the wiringavoids the first transfer transistor TX3 and the second pixel 500 isconnected to the first pixel 400 to share one reading circuit.

As shown in FIG. 9 , in the two pixels (including the first pixel 400and a third pixel 600, wherein for ease of description, another firstpixel adjacent to the second pixel 500 in FIG. 9 is referred to as thethird pixel 600) adjacent to the second pixel 500, a distance D5 betweenthe switching transistor SW and the first floating diffusion region ofthe third pixel 600 is considered as a distance between the switchingtransistor SW and the third pixel 600, a distance D4 between theswitching transistor SW and the first floating diffusion region of thefirst pixel 400 is considered as a distance between the switchingtransistor SW and the first pixel 400. Because a projection of thedistance D5 in the first direction is shorter than a projection of thedistance D4 in the first direction, the first floating diffusion regionof the third pixel 600 will be greatly affected when the switchingtransistor SW is turned on and turned off . Therefore, the second pixel500 and the first pixel 400 (instead of the third pixel 600) in thisembodiment are selected to form the pixel unit. Because the projectionof the distance D4 in the first direction is greater than the projectionof the distance D5 in the first direction, the impact on the firstfloating diffusion region of the first pixel 400 is minor when theswitching transistor SW is turned on and turned off. In addition, whenthe switching transistor SW is connected to the reset transistor RST3through the wiring, the wiring does not pass through the first transfertransistor of the first pixel, thereby reducing the influence onsignals.

In an embodiment, in one pixel unit, a distance between the first sourcefollower transistor SF3 of the first pixel 400 and the second pixel 500is set to be less than a distance between the first row selecttransistor SEL3 of the first pixel 400 and the second pixel 500. Asshown in FIG. 10 , the first pixel 400 and the second pixel 500 areselected to form the pixel unit, to obtain a better layout and improvethe performance of the image sensor

In an embodiment, as shown in FIG. 9 , each second photoelectricconversion element PD4 is disposed at a center of a pattern formed byfour first photoelectric conversion elements PD3 arranged in an array,and the second transfer transistor TX4 and the switching transistor SWare sequentially arranged between two adjacent second photoelectricconversion elements PD4 along the first direction. The first resettransistor RST3, the first source follower transistor SF3, the first rowselect transistor SEL3 are arranged between two adjacent secondphotoelectric conversion elements PD4 along the second directionperpendicular to the first direction. Further, each of four cornerregions of each first photoelectric conversion element PD3(in thisembodiment, PD3 has four corners) is also correspondingly provided witha second photoelectric conversion element PD4, and each of four cornerregions of each second photoelectric conversion element PD4(in thisembodiment, PD4 has four corners) is also correspondingly provided witha first photoelectric conversion element PD3.

In an embodiment, when the pixel unit further includes a dual conversiongain control transistor DCG2. The dual conversion gain controltransistor DCG2 and the first reset transistor RST3 are arranged in acolumn along the second direction, the first source follower transistorSF3 and the first row select transistor SEL3 are arranged in a columnalong the second direction, and the dual conversion gain controltransistor DCG2 and the first reset transistor RST3 are arranged closeto the first photoelectric conversion element PD3 in a same pixel unit.Among them, the gain control transistor DCG2, the first reset transistorRST3 and the first photoelectric conversion element PD3 are arranged inthe first pixel 400.

In an embodiment, the pixel unit further includes a substrate contactSUB. The substrate contact SUB is disposed on a side of the secondphotoelectric conversion element PD4 along the second direction, theside of the second photoelectric conversion element PD4 is facing awayfrom the second transfer transistor TX4. That is, the substrate contactSUB is disposed in a region between the first photoelectric conversionelement PD3 and second photoelectric conversion element PD4, and thefirst photoelectric conversion element PD3 and second photoelectricconversion element PD4 are in one pixel unit. Under a certain potential,a potential barrier for the flow of electrons is formed on the substratecontact SUB, and the potential barrier may effectively block the leakageof electrons in the first pixel 400 to the surrounding second pixels500, thereby isolating the first pixel 400 from the second pixel 500.

In an embodiment, in one pixel unit, a distance between a projection ofa center of the first photoelectric conversion element PD3 in the seconddirection and a projection of a center of the second photoelectricconversion element PD4 in the second direction is a first distance P1.In two adjacent pixel units, a distance between a projection of a centerof the first photoelectric conversion element PD3 of one pixel unit inthe second direction and a projection of a center of the secondphotoelectric conversion element PD4 of the other pixel unit in thesecond direction is a second distance P2. The first distance P1 islarger than the second distance P2. In the embodiment, in one pixelunit, the first photoelectric conversion element PD3 is relatively faraway from the second photoelectric conversion element PD4, so that whenelectrons are being leaked, paths for electrons to leak from the firstphotoelectric conversion element PD3 to the second photoelectricconversion element PD4 are also longer, so that leaked electrons aremore easily absorbed by the voltage terminal VDD of the same first pixelThat is, because the voltage terminal VDD is closer to the firstphotoelectric conversion element PD1, part of electrons leaked from thefirst photoelectric conversion element PD3 flows to the voltage terminalVDD. Therefore, the number of electrons leaked from the firstphotoelectric conversion element PD3 to the second photoelectricconversion element PD4 is reduced, which improve the image accuracy.

In an embodiment, in one pixel unit, a distance between the projectionof the center of the first photoelectric conversion element PD3 in thefirst direction and the projection of the center of the secondphotoelectric conversion element PD4 in the first direction is a thirddistance N1. In two adjacent pixel units, a distance between theprojection of the center of the first photoelectric conversion elementPD3 of one pixel unit in the first direction and the projection of thecenter of the second photoelectric conversion element PD4 of the otherpixel unit in the first direction is a fourth distance N2. The thirddistance N1 is equal to the fourth distance N2

In an embodiment, an area of the first photoelectric conversion elementPD3 is larger than that of the second photoelectric conversion elementPD4, so that the sensitivity of the second photoelectric conversionelement PD4 is lower than that of the first photoelectric conversionelement PD3.

In an embodiment, the pixel structure also includes one or more anattenuation layers, and there is at least one anti-reflection layerdisposed between the second photoelectric conversion element PD4 and anincident light, so that the sensitivity of the second photoelectricconversion element PD4 is lower than that of the first photoelectricconversion element PD3. The attenuation layer may adopt existingattenuation structures. For example, an material layer, or a metal gridare arranged between the photoelectric conversion element and theincident light. The attenuation layer is facing a light-receivingsurface of the second photoelectric conversion element PD4. In anotherembodiment, the attenuation layer may be further extended to the firstphotoelectric conversion element PD3.

In an embodiment, in one pixel unit, the first pixel 400 and the secondpixel 500 are respectively provided with a color filter of the samecolor. For example, multiple first pixels 400 may form a Bayer arrayarrangement, and multiple second pixels 500 may form a Bayer arrayarrangement. The other color filters may be configured according toactual needs. In the embodiment, the first pixel 400 and the secondpixel 500 of one pixel unit are respectively provided with a colorfilter of the same color. That is, color filters of the same color areconfigured on the first photoelectric conversion element PD3 and thesecond photoelectric conversion element PD4 in one pixel unit

In an embodiment, in one pixel unit, the first pixel 400 corresponds toa first lens, and the second pixel 500 corresponds to a second lens. Inthe embodiment, each of the first pixels 400 corresponds to acorresponding one of the first lenses, and each of the second pixels 500corresponds to a corresponding one of the second lenses. The first lensand the second lens may be different, for example, the height of thefirst lens is different from that of the second lens.

In an embodiment, as shown in FIG. 8 , the pixel unit includes a chargestorage device. A terminal of the charge storage device is coupled tothe second floating diffusion region, the other terminal of the chargestorage device is connected to ground or a variable voltage.

In an embodiment, the charge storage device is a capacitor C2. Thecharge storage device is used to storage charges generated by the secondphotoelectric conversion element PD2, to increase a full well capacityof the second pixel 500 and to reduce the sensitivity of thephotoelectric conversion element. Optionally, the capacitor C2 is adevice capacitance or a parasitic capacitance.

The present disclosure provides an image sensor. The image sensorincludes the pixel structure described in the above embodiments. Theimage sensor may be a complementary metal oxide semiconductor (CMOS)image sensor, or may be other image sensors that may use pixelstructures described in the above embodiments.

The present disclosure also provides an electronic device. Theelectronic device includes the image sensor described in the aboveembodiments. The electronic device may be a mobile device, a digitalcamera, a medical device, or a computer. The electronic device includesthe image sensor. The specific structure of the image sensor refers tothe above embodiments. Since the electronic device device adopts all thetechnical solutions of all the above embodiments, it has at least allthe beneficial effects brought by the technical solutions of the aboveembodiments. In addition, the electronic equipment may also bemonitoring equipment, machine vision related device, UAV, mobile phones,cameras, and the like.

As shown in FIGS. 11-12 , the present disclosure also provides a methodfor controlling an image sensor, which is applicable to the image sensordescribed in the above embodiments. The method includes step 210 andstep 220:

Step 210, reading information of the first pixel 400, where the firstpixel 400 includes the first photoelectric conversion element PD3 andthe first transfer transistor TX3. The step 210 of reading informationof the first pixel 400 includes step 211 and step 212.

Step 211, resetting a storage region of the first pixel 400, andquantizing it to obtain a first reset signal Vrst1.

Step 212, transferring image information of the first photoelectricconversion element PD3, and quantizing it to obtain a first imagesampling signal Vsig1.

Step 220, reading information of the second pixel 500, where the secondpixel 500 includes the second photoelectric conversion element PD4 andthe second transfer transistor TX4. The step 220 of reading informationof the second pixel 500 includes step 221.

Step 221, transferring image information of the first photoelectricconversion element PD4, and quantizing it to obtain a second imagesampling signal Vsig2.

a first actual image signal of the first pixel 400 is obtained based onthe first reset signal Vrst1 and the first image sampling signal Vsig1,and a second actual image signal of the second pixel 500 is obtainedbased on the second image sampling signal Vsig2. It should be noted thatthe execution sequence of steps 111, 112, and 121 does not strictlyrepresent the execution sequence of each step of the method in thepresent disclosure, and those skilled in the art may change theexecution sequence of the above steps according to actual needs. Basedon a reading mode of the first pixel, the CDS may be realized.

In an embodiment, step 120 of reading information of the second pixel500 also includes:

Step 122, resetting a storage region of the second pixel 500, andquantizing it to obtain a second reset signal Vrst2; and obtaining asecond actual image signal based on the second reset signal Vrst2 andthe second image sampling signal Vsig2.

In an embodiment, as shown in FIG. 11 , the step of quantifying thereset signal may be performed after step 121. In another embodiment, asshown in FIG. 12 , the step of quantifying the reset signal may beperformed after step 112 and before step 121. In FIGS. 11-12 , 3 µmpixel is an example of the first pixel 400, 1.0 µm pixel is an exampleof the second pixel 500.

In an embodiment, the reading mode of the first pixel 400 includes atleast one of a low conversion gain mode and a high conversion gain mode.The first pixel is read in the low conversion gain mode (as shown inFIG. 4 ), or is read in the high conversion gain mode (as shown in FIG.5 ), or is read in both the low conversion gain mode and the highconversion gain mode (as shown in FIG. 11 and FIG. 12 ). The highdynamic range is achieved in the above reading modes. In an embodiment,the high conversion gain mode and the low conversion gain mode may berealized by preparing the conversion gain transistor DCG2 between thereset transistor RST3 and the first floating diffusion region. In afurther embodiment, the high conversion gain mode and the low conversiongain mode may be realized by preparing a capacitor between the resettransistor RST3 and the dual conversion gain transistor DCG2, switchingbetween the high conversion gain mode and the low conversion gain modemay be realized by turning on or turning off the dual conversion gaintransistor DCG2. In other embodiments, other methods may be adopted toswitch between the high conversion gain mode and the low conversion gainmode.

As shown in FIG. 11 and FIG. 12 , when the first pixel 400 is read inthe high conversion gain mode and the low conversion gain mode, themethod of reading the first pixel 400 includes following steps:

Step 213, resetting the storage area of the first pixel in the lowconversion gain mode LCG, and quantizing it to obtain the first resetsignal lcgrst1 in the low conversion gain mode LCG.

Step 214, resetting the storage area of the first pixel in the highconversion gain mode HCG, and quantizing it to obtain the first resetsignal hcgrst1 in the high conversion gain mode HCG.

Step 215, transferring image information of the first photoelectricconversion element in the high conversion gain mode HCG, and quantizingit to obtain the first image sampling signal hcgsig1 in the highconversion gain mode HCG.

Step 216, redistributing image information of the first photoelectricconversion element in the low conversion gain mode LCG, and quantizingit to obtain the first image sampling signal lcgsig1 in the lowconversion gain mode LCG.

The first actual image signal of the first pixel is obtained based onthe first reset signal lcgrst1 and the first image sampling signallcgsig1 in the low conversion gain mode, and the first reset signalhcgrst1 and the first image sampling signal hcgsig1 in the highconversion gain mode. It should be noted that the method of reading thefirst pixel in the low conversion gain mode of the high conversion gainmode refers to FIG. 4 and FIG. 5 in the embodiment 1.

As shown in FIG. 11 , one method of reading the second pixel 500includes following steps: image information of the second photoelectricconversion element is transferred, the second image sampling signalVsig2 is obtained by quantizing, and then the storage area of the secondpixel is reset, and the second reset signal Vrst2 is obtained byquantizing. FIG. 11 shows a signal transmission timing with theswitching transistor SW. As shown in FIG. 12 , another method of readingthe second pixel 500 includes following steps: the storage area of thesecond pixel is reset, the second reset signal Vrst2 is obtained byquantizing, and then the image information of the second photoelectricconversion element is transferred, and the second image sampling signalVsig2 is obtained by quantizing; based on this above method of readingthe second pixel 500, the CDS may be realized. FIG. 12 shows a signaltransmission timing without the switching transistor SW and a signaltransmission timing with the switching transistor SW (the timing of theswitching transistor SW in FIG. 12 is shown by a dotted line) Otherexecution sequences of the above steps may also be used to read out thesecond pixel

As described above, the pixel structure, the image sensor, theelectronic device and the method for controlling an image sensor in thepresent disclosure have the following beneficial effects:

The present disclosure adopts the first photoelectric conversion elementand the second photoelectric conversion element, which have differentsensitivities The first photoelectric conversion element has highsensitivity (due to, e.g., a large area), which is mainly used to obtainweak light information, and the second photoelectric conversion elementhas low sensitivity (due to, e.g., a small area), which is mainly usedto obtain strong light information. Therefore, the image sensor of thepresent disclosure is able to recognize strong light information and lowlight information, which improves its dynamic range.

The present disclosure designs the layout of the pixel structure, whichmay effectively reduce a signal noise, improve a reading accuracy, andreduce the amount of electrons flowing from the large-area firstphotoelectric conversion element to the small-area second photoelectricconversion element, thereby improving the performance of the imagesensor

In summary, the present disclosure effectively overcomes various defectsin the prior art and has a high industrial value.

The above-mentioned embodiments are merely illustrative of the principleand effects of the present disclosure instead of limiting the presentdisclosure. Modifications or variations of the above-describedembodiments may be made by those skilled in the art without departingfrom the spirit and scope of the present disclosure. Therefore, allequivalent modifications or changes made by those who have commonknowledge in the art without departing from the spirit and technicalconcept disclosed by the present disclosure shall be still covered bythe claims of the present disclosure.

What is claimed is:
 1. A pixel structure, wherein the pixel structurecomprises a plurality of pixel units arranged in an array, and eachpixel unit comprises: a first photoelectric conversion element; a firsttransfer transistor, coupled to a first floating diffusion region, fortransferring charges in the first photoelectric conversion element tothe first floating diffusion region; a second photoelectric conversionelement, wherein the sensitivity of the second photoelectric conversionelement is lower than that of the first photoelectric conversionelement; a second transfer transistor, coupled to a second floatingdiffusion region, for transferring charges in the second photoelectncconversion element to the second floating diffusion region; and areading circuit, coupled to the first floating diffusion region and thesecond floating diffusion region, for reading voltage signals of thefirst floating diffusion region and the second floating diffusionregion.
 2. The pixel structure according to claim 1, wherein the readingcircuit comprises: a first reset transistor, wherein a source of thefirst reset transistor is coupled to the first floating diffusionregion, a drain of the first reset transistor is coupled to a firstvoltage terminal, and the first reset transistor is for resetting thefirst floating diffusion region; a first source follower transistor,wherein a gate of the first source follower transistor is coupled to thefirst floating diffusion region, a drain of the first source followertransistor is coupled to a second voltage terminal, and a source of thefirst source follower transistor is coupled to a first output line; asecond reset transistor, wherein a source of the second reset transistoris coupled to the second floating diffusion region, a drain of thesecond reset transistor is coupled to a third voltage terminal, and thesecond reset transistor is for resetting the second floating diffusionregion; and a second source follower transistor, wherein a gate of thesecond source follower transistor is coupled to the second floatingdiffusion region, a drain of the second source follower transistor iscoupled to a fourth voltage terminal, a source of the second sourcefollower transistor is coupled to a second output line.
 3. The pixelstructure according to claim 2, wherein the first voltage terminal, thesecond voltage terminal, the third voltage terminal and the fourthvoltage terminal are the same voltage terminal; and/or, the first outputline and the second output line is the same output line.
 4. The pixelstructure according to claim 2, wherein the reading circuit comprises: afirst row select transistor, wherein a drain of the first row selecttransistor is coupled to the source of the first source followertransistor, and a source of the first row select transistor is coupledto the first output line, and a second row select transistor, wherein adrain of the second row select transistor is coupled to the source ofthe second source follower transistor, and a source of the second rowselect transistor is coupled to the second output line, and/or a doubleconversion gain control transistor, coupled between the first floatingdiffusion region and the first reset transistor.
 5. The pixel structureaccording to claim 4, wherein a first pixel comprises the firstphotoelectnc conversion element, the first transfer transistor, thefirst floating diffusion region, the first reset transistor, the firstsource follower transistor, and the first row select transistor,multiple first pixels arranged in a first direction; a second pixelcomprises the second photoelectric conversion element, the secondtransfer transistor, the second floating diffusion, the second resettransistor, the second source follower transistor, and the second rowselect transistor, multiple second pixels arranged in a first direction;a plurality of first pixels are arranged in an array, and a plurality ofsecond pixels are arranged in an array, wherein the first pixel and thesecond pixel adjacent to the first pixel form a pixel unit, wherein adistance between a projection of the first row select transistor of thefirst pixel in a first direction and a projection of the second rowselect transistor of the second pixel in the first direction is shorterthan those between the projection of the first row select transistor ofthe first pixel in the first direction and projections of second rowselect transistors of other pixels in the first direction.
 6. The pixelstructure according to claim 5, wherein in one pixel unit, a distancebetween the first source follower transistor of the first pixel and thesecond pixel is set to be less than a distance between the first rowselect transistor of the first pixel and the second pixel.
 7. The pixelstructure according to claim 5, wherein each second photoelectricconversion element is disposed at a center of a pattern formed by fourfirst photoelectric conversion elements arranged in an array, the secondtransfer transistor, the second reset transistor, the second sourcefollower transistor and the second row select transistors aresequentially arranged between two adjacent second photoelectricconversion elements along the first direction; the first resettransistor, the first source follower transistor, the first row selecttransistors are arranged between two adjacent second photoelectricconversion elements along a second direction perpendicular to the firstdirection.
 8. The pixel structure according to claim 7, wherein when thepixel unit further comprises a dual conversion gain control transistor,the dual conversion gain control transistor and the first resettransistor are arranged in a column along the second direction, thefirst source follower transistor and the first row select transistor arearranged in a column along the second direction, and the gain controltransistor and the first reset transistor are arranged close to thefirst photoelectric conversion element in a same pixel unit, wherein thedual conversion gain control transistor, the first reset transistor andthe first photoelectric conversion element are arranged in one firstpixel.
 9. The pixel structure according to claim 8, wherein the pixelunit further comprises: a substrate contact, wherein the substratecontact is disposed on a side of the first row select transistor alongthe second direction, the side of the first row select transistor isfacing away from the first source follower transistor.
 10. The pixelstructure according to claim 5, wherein in one pixel unit, a distancebetween a projection of a center of the first photoelectric conversionelement in the second direction and a projection of a center of thesecond photoelectric conversion element in the second direction is afirst distance; In two adjacent pixel units, a distance between aprojection of a center of the first photoelectric conversion element ofone pixel unit in the second direction and a projection of a center ofthe second photoelectric conversion element of the other pixel unit inthe second direction is a second distance; the first distance is largerthan the second distance; and/or, in one pixel unit, a distance betweenthe projection of the center of the first photoelectric conversionelement in the first direction and the projection of the center of thesecond photoelectric conversion element in the first direction is athird distance; in two adjacent pixel units, a distance between theprojection of the center of the first photoelectric conversion elementof one pixel unit in the first direction and the projection of thecenter of the second photoelectnc conversion element of the other pixelunit in the first direction is the fourth distance, wherein the thirddistance is equal to the fourth distance.
 11. The pixel structureaccording to claim 1, wherein the reading circuit comprises: a resettransistor, wherein a source of the reset transistor is coupled to thefirst floating diffusion region and the second floating diffusion regionrespectively, a drain of the reset transistor is coupled to a firstcommon terminal, the reset transistor is for resetting the firstfloating diffusion region and the second floating diffusion region; anda source follower transistor, a gate of the source follower transistoris coupled to the first floating diffusion region and the secondfloating diffusion region respectively, a drain of the source followertransistor is coupled to a second common terminal, a source of thesource follower transistor is coupled to an output line.
 12. The pixelstructure according to claim 11, wherein the reading circuit comprises:a switching transistor, wherein the source of the reset transistor iscoupled to the second floating diffusion region through the switchingtransistor, and a gate of the source follower transistor is coupled tothe second floating diffusion region through the switching transistor,and/or a gain control transistor, coupled between the first floatingdiffusion region and the reset transistor.
 13. The pixel structureaccording to claim 11, wherein the reading circuit further comprises arow select transistor, wherein a drain of the row select transistor iscoupled to the source of the source follower transistor, and a source ofthe row select transistor is coupled to the output line; wherein a firstpixel comprises the first photoelectric conversion element, the firsttransfer transistor, and the first floating diffusion region, multiplefirst pixels arranged in a first direction; a second pixel comprises thesecond photoelectric conversion element, the second transfer transistor,the second floating diffusion region, the second reset transistor, thesecond source follower transistor and the second row select transistor,multiple first pixels arranged in a first direction; a plurality of thefirst pixel are arranged in an array, and a plurality of the secondpixel are arranged in an array, wherein the first pixel and the secondpixel adjacent to the first pixel form a pixel unit, wherein a lineconnecting a projection of the first floating diffusion region of thefirst pixel in the first direction to a projection of the secondfloating diffusion region of the second pixel in the first directiondoes not intersect a projection of the first transfer transistor in thefirst direction.
 14. The pixel structure according to claim 13, when thereading circuit includes a switching transistor, wherein the switchingtransistor is disposed on a side of the second transfer transistor alongthe first direction, the side of the second transfer transistor isfacing away from the second photoelectric conversion element, whereinthe second pixel and the first pixel adjacent to the second pixel formthe pixel unit, wherein a distance between a projection of the firstfloating diffusion region of the first pixel in the first direction anda projection of the switching transistor of the second pixel in thefirst direction is further than those between projections of the firstfloating diffusion regions of a plurality of pixels adjacent to thesecond pixel in the first direction and the projection of the switchingtransistor of the second pixel in the first direction.
 15. The pixelstructure according to claim 13, wherein in one pixel unit, a distancebetween the first source follower transistor of the first pixel and thesecond pixel is set to be less than a distance between the first rowselect transistor of the first pixel and the second pixel.
 16. The pixelstructure according to claim 13, wherein each second photoelectricconversion element is disposed at a center of a pattern formed by fourfirst photoelectric conversion elements arranged in an array, the secondtransfer transistor and the switching transistor are sequentiallyarranged between two adjacent second photoelectric conversion elementsalong the first direction, the first reset transistor, the first sourcefollower transistor, the first row select transistors are arrangedbetween two adjacent second photoelectric conversion elements along asecond direction perpendicular to the first direction.
 17. The pixelstructure according to claim 16, wherein when the pixel unit furthercomprises a dual conversion gain control transistor, the dual conversiongain control transistor and the first reset transistor are arranged arearranged in a column along the second direction, the first sourcefollower transistor and the first row select transistor are arranged ina column along the second direction, and the dual conversion gaincontrol transistor and the first reset transistor are arranged close tothe first photoelectric conversion element in a same pixel unit, whereinthe gain control transistor, the first reset transistor and the firstphotoelectric conversion element are arranged in one first pixel. 18.The pixel structure according to claim 17, wherein the pixel unitfurther comprises: a substrate contact, wherein the substrate contact isdisposed on a side of the second photoelectric conversion element alongthe second direction, the side of the second photoelectric conversionelement is facing away from the second transfer transistor.
 19. Thepixel structure according to claim 16, wherein in one pixel unit, adistance between a projection of a center of the first photoelectricconversion element in the second direction and a projection of a centerof the second photoelectric conversion element in the second directionis a first distance; In two adjacent pixel units, a distance between aprojection of a center of the first photoelectric conversion element ofone pixel unit in the second direction and a projection of a center ofthe second photoelectric conversion element of the other pixel unit inthe second direction is a second distance; the first distance is largerthan the second distance; and/or, in one pixel unit, a distance betweenthe projection of the center of the first photoelectric conversionelement in the first direction and the projection of the center of thesecond photoelectric conversion element in the first direction is athird distance; in two adjacent pixel units, a distance between theprojection of the center of the first photoelectric conversion elementof one pixel unit in the first direction and the projection of thecenter of the second photoelectric conversion element of the other pixelunit in the first direction is the fourth distance, wherein the thirddistance is equal to the fourth distance.
 20. The pixel structureaccording to claim 1, further comprising: at least one attenuationlayer, wherein there is at least one attenuation layer is disposedbetween the second photoelectric conversion element and an incidentlight; and/or an area of the first photoelectric conversion element islarger than that of the second photoelectric conversion element.
 21. Thepixel structure according to claim 1, wherein in one pixel unit, thefirst pixel and the second pixel are provided with a color filter of thesame color respectively, and/or, in one pixel unit, the first pixelcorresponds to a first lens, the second pixel corresponds to a secondlens.
 22. The pixel structure according to claim 1, wherein the pixelunit further comprises a charge storage device, one terminal of thecharge storage device is coupled to the second floating diffusionregion, and the other terminal of the charge storage device is connectedto ground or a variable voltage.
 23. An image sensor, comprising: apixel structure as claimed in claim 1, and a peripheral logic circuitfor receiving and processing signals output by a reading circuit of thepixel structure.
 24. A method for controlling an image sensor,applicable to the image sensor as claimed in claim 26, comprising:reading information of a first pixel, wherein the first pixel comprisesa first photoelectric conversion element and a first transfertransistor; wherein the step of reading information of a first pixelcomprises: resetting a storage region of the first pixel, and quantizingit to obtain a first reset signal, transferring image information of thefirst photoelectric conversion element, and quantizing it to obtain afirst image sampling signal; reading information of a second pixel,wherein the second pixel comprises a second photoelectric conversionelement and a second transfer transistor wherein the step of readinginformation of a second pixel comprises transferring image informationof the second photoelectric conversion element, and quantizing it toobtain a second image sampling signal; wherein, a first actual imagesignal of the first pixel is obtained based on the first reset signaland the first image sampling signal, and a second actual image signal ofthe second pixel is obtained based on the second image sampling signal.25. The method for controlling an image sensor according to claim 24,the step of reading information of a second pixel also comprises:resetting a storage region of the second pixel, and quantizing it toobtain a second reset signal, and quantizing it to obtain a secondactual image signal based on the second image reset signal and thesecond image sampling signal.
 26. The method for controlling an imagesensor according to claim 24, wherein the reading mode of the firstpixel comprises at least one of a low conversion gain mode and a highconversion gain mode, when the first pixel is read in both the lowconversion gain mode and the high conversion gain mode, the step ofreading information of a first pixel comprise following steps: resettingthe storage area of the first pixel in the low conversion gain mode, andquantizing it to obtain the first reset signal in the low conversiongain mode; resetting the storage area of the first pixel in the highconversion gain mode, and quantizing it to obtain the first reset signalin the high conversion gain mode; transferring image information of thefirst photoelectric conversion element in the high conversion gain mode,and quantizing it to obtain the first image sampling signal in the highconversion gain mode; redistributing image information of the firstphotoelectric conversion element in the low conversion gain mode, andquantizing it to obtain the first image sampling signal in the lowconversion gain mode; wherein, the first actual image signal of thefirst pixel is obtained, based on the first reset signal and the firstimage sampling signal in the low conversion gain mode, and the firstreset signal and the first image sampling signal in the high conversiongain mode.